This invention relates to epoxy resin compositions of inorganic filler loading type suitable as a sealing material for optical semiconductor and affording cured products having high transparency in various temperature environments, and semiconductor devices sealed with the compositions in a cured state.
While the recent advance of the information technology requires effective transmission and processing of a vast quantity of information bits, what is now under investigation as a substitute for conventional signal transmission through electrical wiring is semiconductor devices which take advantage of the high speed, low loss, non-induction and other desirable features of optical signals and mounting technology used therefor.
Most of prior art opto-functional devices are sealed with epoxy resins which are free of inorganic filler in order that the resin layer be transparent. Such unfilled epoxy resins are not satisfactory when the heat resistance, humidity resistance and low stress property of cured parts are taken into account. There is a need for a transparent sealant which contains an inorganic filler.
An object of the invention is to provide a light-transmissive epoxy resin composition of inorganic filler loading type which is suitable as a sealing material for optical semiconductor and affords cured products maintaining high transparency in various temperature environments. Another object is to provide a semiconductor device sealed with the epoxy resin composition.
It has been found that when an epoxy resin composition comprising an epoxy resin, a curing accelerator, and an inorganic filler as essential components satisfies both the relationships of the following formulae (1) and (2), cured products thereof maintain high transparency in varying temperature environments.
Accordingly, the invention provides a light-transmissive epoxy resin composition comprising (A) an epoxy resin, (B) a curing accelerator, and (C) an inorganic filler, wherein the composition satisfies both the relationships of the following formulae (1) and (2).
[{2(nA2+nC2)xe2x88x92(nA+nC)2}/2]xc2xd less than 3.0xc3x9710xe2x88x923xe2x80x83xe2x80x83(1) 
[{2(fA2+fC2)xe2x88x92(fA+fC)2}/2]xc2xd less than 1.0xc3x9710xe2x88x925xe2x80x83xe2x80x83(2) 
Herein nA is the refractive index at T1xc2x0 C. of the cured product of the composition excluding the inorganic filler,
nC is the refractive index at T1xc2x0 C. of the inorganic filler,
fA is a temperature coefficient of the refractive index of the cured product of the composition excluding the inorganic filler,
fC is a temperature coefficient of the refractive index of the inorganic filler, and
the temperature coefficient of refractive index is given by the formula (3):
f={n(T2)/n(T1)xe2x88x921}/(T2xe2x88x92T1)xe2x80x83xe2x80x83(3) 
wherein n(T1) is the refractive index at T1xc2x0 C. and n(T2) is the refractive index at T2xc2x0 C., with the proviso that T1 less than T2. 
Also provided is a semiconductor device sealed with the epoxy resin composition in a cured state.